Solvolysis of 1-(X-phenyl)-1-cyclohexyl chlorides in methanol/acetonit
rile mixtures was studied at 30.0 and 40.0 degrees C. The rho(x)(+) va
lues, -4.67 to -4.81 at 30.0 OC, are within the range of rho(x)(+) for
the solvolysis of secondary and tertiary compounds, which are believe
d to react by an S(N)1 mechanism. Relatively large slopes (m greater t
han or equal to 1.0) of the Grunwald-Winstein mY(1-AdOTS) plots sugges
t that the positive charge developed in the transition state is consid
erable and is delocalized onto the aromatic ring. The cross-interactio
n constant Theta (= partial derivative m/partial derivative sigma(X) =
partial derivative rho(X)(+) Y) is positive and nonnegligible (+0.54)
, which indicates that the solvent effect on the localized charge (par
tial derivative Y>0) is the opposite of that on the delocalized positi
ve charge (delta rho(X)(+)>0 or delta(-rho(X)(+))<0). Solvent isotope
effects (k(H)/k(D) = 1.12-1.17 at 40.0 degrees C), weak common-ion mas
s-law effects, and the range of activation parameters (Delta H-not equ
al = 18-22 kcal mol(-1) and Delta S-not equal = -1 to -15 cat mol(-1)
K-1) are all consistent with the proposed S(N)1 mechanism.